Process of generating nitrogen using metal azide

ABSTRACT

A METHOD OF GENERATING HOT NITROGEN GAS COMPRISING CONTACTING SF6 OR N2O WITH SODIUM AZIDE OR AN AZIDE OF SIMILAR SENSITIVITY IN THE PRESENCE OF A CONVENTIONAL PROPELLANT INITIATOR.

, [P OCESS or U'.S. Cl. 423-351 3,773,947 GENERATING NITROGEN USING METAL AZIDE earn-Bayes and Carl T. Zovko, Silver Spring, Md.,

' assignors'to the United States of America, as represented by the Secretary of the Navy NoDrawing. Filed 'Oct. 13, 1972, Ser. No. 297,512

Int. Cl. C01b 21/00 12 Claims j' ABSTRACT OF THE DISCLOSURE .BACKGROUND OF THE INVENTION This invention generally relates to a gas generator and more particularly to 'a hybrid nitrogen gas generator.

'Currently nitrogen gas generators find use in the fields of electric power, mechanical work, pressurization of liquid propellants and as a fuel source for gas dynamic lasers. Gas dynamic 'la'sers utilizing gas compositions which are mainly N have been operated by are heating of thegas which had been stored as a gas under pressure oras a cryogenic liquid or else by the combustion of preheated CO with with subsequent addition of N from the same sources. However any system of furnishing the iigascorn position which depends on pressurized or cryogenic N is undesirably bulky and inconvenient.

Some nitrogen gas generators are based on the reaction of NaN with F ClF N O4or other similar materials to produce N but use of these toxic, corrosive gases and liquids haveproven to be unacceptably hazardous to personnel.,

Thus research has been conducted in an attempt to find a'relatively safe method of producing nitrogen which does not,requirethe use of bulky, inconvenient equipment.

SUMMARY OF THE INVENTION Accordingly one object of this invention is to provide a new method of generating nitrogen.

Another object of this invention is to provide a method for generating nitrogen without using bulky, inconvenient cryogenic equipment.

A still further object of this invention is to provide a method of generating nitrogen which does not use toxic or corrosive materials which are hazardous to personnel.

Yet another object of this invention is to provide a method of generating pure nitrogen which nitrogen can be used in gas dynamic lasers.

A still further object of this invention is to provide nitrogen which can be used in the fields of electrical power. Mechanical work and pressurization of liquid propellants.

These and other objects of this invention are accomplished by providing a method of generating nitrogen comprising contacting sodium azide or an azide of similar sensitivity, with SF N 0, or an oxygen containing gas (i.e. air or pure oxygen) in the presence of a conventional solid propellant initiator.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention comprises a method of generating nitrogen, which can be used in any or all of the hereinbefore noted fields, by contacting sodium azide with SP N 0 or an oxygen containing gas in the presence of a conventional propellant initiator. In this method the fuel and the oxidizer are not mixed until they are burned.

United States Patent 0 3,773,947 Patented Nov. 20, 1973 The fuel, sodium azide, is present in the combustion chamber of the gas generating apparatus as a solid grain and the oxidizer, which can be a liquid such as SP or N 0, or a gas which contains oxygen is stored in a separate container and pumped into the combustion chamber at the appropriate rate when the burning is started. If CO is desired, as in the case of use of N in the gas dynamic laser wherein it is desirable for the gas being generated to comprise about 80-90% N 10-15% CO and 12% water, it may be added after N generation or it may be supplied by adding a carbonate or other combination of CO generating materials such as carbon and sodium nitrate, to the sodium azide.

Since the azide and SP N 0 and oxygen containing gas are not hypergolic it is necessary to have an igniter present to start the reaction. Reaction is started by burning a small conventional solid propellant ignitor in the combustion chamber in the presence of both SF N 0 or the oxygen containing gas and the azide. The SP or N 0 which are preferred oxidizers, can be made to contact the azide either as a gas or a liquid. The stoichiometric reaction between sodium axide and SP is while the stoichiometric reaction between sodium azide and N 0 is 2NaN3 N320 4N2 In situations where it is desirable to have as few products in addition to N present it is preferred to have about stoichiometric amounts of the azide and the SF N 0 or oxygen. However for most uses it is only necessary to have some quantity of the fuel and oxidizer present. In practice it is desirable, from the point of efl'iciency, to have one of the two constituents present in an amount approximately of the stoichiometric molar amounts and it is most desirable that one of the constituents not be present in any quantity less than 20% of the stoichiometric quantity.

As seen above the chemical reactions which produce N also produce other products (i.e., NaF, Na s etc.). For some uses, such as in a gas dynamic laser, these impurities should be removed before the gas enters the laser becaue impurities of this type can plug the nozzle, absorb or scatter light or coat the optical components. The solid and/or liquid impurities can be removed by any of the conventional techniques such as, for example, by passing the gas through a series of baffles while the gas is still at high pressure and low velocity. The entrained particles will not follow the same path as the gas stream and they will impinge on the walls and be trapped.

It should be noted that other azides besides sodium azide may be used in the process of this invention provided that the azide has similar sensitivity to sodium azide. A specific azide which may be used is lithium azide.

The conventional solid propellant ignitor which is used to initiate reaction need only be present in extremely small quantities because once the reaction is started it no longer requires the presence of the ignitor. Any of the well known solid propellant ignitors can be used. Some examples of these ignitors are black powder, pyrotechnics, metal oxident mixtures such as boron/KNOg, aluminum/ potassium perchlorate, thermites etc. The exact nature of the ignitor is immaterial since its only function is to start the reaction. Thus the ignitor is a separate device which contains any of the art recognized solid propellant initiators and which is either contained in or vented into the combustion chamber.

The general nature of the invention having been set forth, the following example is presented as a specific illustration thereof. It will be understood that the invention is not limited to this example but is susceptible to various modifications that will be recognized by one of ordinary skill in the art.

EXAMPLE A small, general purpose, vented, combustion chamber with an exhaust nozzle throat area of 0.025 square inches was used to carry out the nitrogen generation. Sodium azide was pressed into a perforated cylinder 2.211 inches O. D., 1.135 inches I.D., and 1.279 inches long. It weighed 100 g. The sulfur hexafluoride was introduced from the top end of the sodium azide cylinder by injecting it through a solid cone spray nozzle. The reaction was initiated by an igniter, JPN propellant, which could pressurize the combustion chamber for 0.2 second at 200 p.s.i. with a gas at 1840 K. The typical results were burn times between and seconds.

Naturally the N 0 can be substituted for SP and any of the standard hybrid gas generator combustion chambers can be used as the reaction vessel. Furthermore oxygen or an oxygen containing gas can also be substituted for the SP and N 0 but as hereinbefore noted the use of SP and N 0 are preferred.

It should also be noted that other constituents can also be added to the azide pellets. A particularly good embodiment involves the use of a mixture of pure azide pellets and pellets which contains azide plus sulfur. In the embodiment it is preferred that the pellet comprise about 90-98% by weight azide and 2-10% by weight sulfur. It is also preferable in this embodiment to geometrically position the azide-sulfur pellets so that the oxidizer first contacts the mixed pellet and then contacts the pure azide pellet. Naturally the ignitor should be positioned so that it is positioned in the combustion chamber or vented into at the point where the mixed pellet is located. More information on the use of an azide-sulfur pellet is contained in copending application Ser. No. 297,513 entitled Nitrogen Generator, by Carl Boyars and Carl T. Zovko filed on the same date herewith and hereby incorporated by reference.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A method of generating nitrogen comprising; contacting an azide fuel selected from the group consisting of sodium azide, lithium azide and mixtures thereof with an oxidant selected from the group consisting of SP N10, and mixtures thereof in the presence of a conventional solid propellant initiator which has been ignited.

2. The method of claim 1 wherein said azide is sodium azide and said oxidant is SF l 3. The method of claim 1 wherein said azide is sodium azide and said oxidant is N 0.

4. The method of claim 1 wherein said fuel and said oxidant are present in about stoichiometric amounts.

5. The method of claim 1 wherein the quantity of one of the two major constituents is at least about 20% of the stoichiometric quantity.

6. The method of claim 5 wherein the quantity of one of the two major constituents is at least about of the stoichiometric quantity.

7. The method of claim 2 wherein said fuel and said oxidant are present in about stoichiometric amounts.

8. The method of claim 3 wherein said fuel and said oxidant are present in about stoichiometric amounts.

9. The method of claim 2 wherein the quantity of one of the two major constituents is at least about 20% of the stoichiometric quantity.

10. The method of claim 3 wherein the quantity of one of the two major constituents is at least about 20% of the stoichiometric quantity.

11. The method of claim 9 wherein the quantity of one of the two major constituents is at least about 75 of the stoichiometric quantity.

12. The method of claim 10 wherein the quantity of one of the two major constituents is at least about 75 of the stoichiometric quantity.

References Cited UNITED STATES PATENTS 4/1961 Boyer 149-36 X 2/ 1964 Kaufman et al. 149-35 

